Dropdown window does not appear and I cannot save login details for https://ycs.agoda.com/en-us/Login even though it saves password in security settings.

When I try to login to this site https://ycs.agoda.com/en-us/Login I have to type in username and password details every time even though Firefox has saved the password in security preferences. Also when I have entered the full username and password to login, the dropdown 'do you want to save password' does not appear. For some reason Firefox does not work to save login details on this website. I have tried with Safari and Chrome and have no problem with those browsers. Computer is Apple OS X El Capitan